Production process of composite pressure pipe electric melting sleeve piece

Abstract

The invention relates to the technical field of electric melting sleeves, and discloses a production process of a composite pressure pipe electric melting sleeve part, which comprises the following steps: S1, preparing raw materials including the following components in parts by mass: 50-60 parts of a base material, 5-10 parts of a filler, 2-4 parts of a hyperbranched polymer, 0.5-1 part of an antioxidant, 1-2 parts of a light stabilizer and 1-3 parts of a metal wire; s2, performing primary injection molding, cooling to room temperature, taking out, and sleeving metal wires on two sides of the inner wall of the inner ring of the sleeve; and S3, secondary injection molding is conducted, specifically, the inner ring of the sleeve is arranged in a second mold, and after the sleeve is cooled to the room temperature, the electric smelting sleeve is taken out. The hyperbranched polymer is distributed in a matrix in a molten state, a compact cross-linked network is formed after cooling, and the material has the characteristics of low viscosity and interaction between macromolecular chains, so that the elongation at break of the material is effectively improved, the material has excellent energy absorption capacity under the action of external force, and the impact resistance is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of electrofusion sleeves, and particularly to a production process for electrofusion sleeve fittings of composite pressure pipes. Background Art

[0002] Electrofusion sleeve fittings for composite pressure pipes are high-performance connectors widely used in industries such as electricity, communication, petroleum, and natural gas. They are mainly used to connect cables or pipes to ensure stable operation in high-temperature and high-pressure environments. The electrofusion sleeve fittings adopt special electrofusion connection technology. During the heating process, heat is transferred through the metal wires inside the sleeve to achieve the purpose of electrofusion connection, ensuring the reliability and safety of the pipeline system. This technology has important application value in fields such as power transmission, communication cable protection, and petroleum and natural gas pipelines, especially for long-term stability and high-load transmission capacity in harsh environments.

[0003] However, there are still some deficiencies in the performance of existing electrofusion sleeve fittings for composite pressure pipes. Traditional electrofusion sleeve fittings usually rely on a single polymer material. Although they have certain strength and thermal stability, they are prone to problems such as fracture, cracking, or uneven heat conduction when facing complex working conditions such as high temperature, impact, or pressure. In addition, the fillers and reinforcing agents commonly used in existing technologies are mostly traditional inorganic materials. Although they can improve the strength and wear resistance of the materials, they have limitations in improving fracture toughness, energy absorption capacity, and thermal conductivity. These technical deficiencies lead to insufficient stability of electrofusion connection and are difficult to meet the industrial application requirements of high strength and high stability. Summary of the Invention

[0004] Aiming at the deficiencies of the existing technology, the present invention provides a production process for electrofusion sleeve fittings of composite pressure pipes, which solves the deficiencies of traditional materials in improving impact toughness, thermal conductivity, and electrofusion stability, and at the same time avoids the problems of internal stress accumulation and unstable material properties caused by uneven cooling.

[0005] To achieve the above objectives, the present invention is realized through the following technical solutions: A production process for electrofusion sleeve fittings of composite pressure pipes includes the following steps:

[0006] S1. Prepare raw materials, and the raw materials include the following components in parts by mass: base material: 50 - 60 parts, filler: 5 - 10 parts, hyperbranched polymer: 2 - 4 parts, antioxidant: 0.5 - 1 part, lubricant: 0.2 - 0.5 part, light stabilizer: 1 - 2 parts, crosslinking agent: 0.5 - 2 parts, metal wire: 1 - 3 parts;

[0007] S2. One - time injection molding: Mix and heat the raw materials to melt them, then pour the molten raw materials into Mold 1, take them out after cooling to room temperature to obtain the inner sleeve ring. Then, set the metal wire inside the inner sleeve ring, and metal wires are arranged on both sides of the inner wall of the inner sleeve ring.

[0008] The mixing and stirring control during the one - time injection molding process is crucial for the uniformity of the raw materials. Appropriate stirring speed and time can ensure the full mixing of components such as fillers and hyper - branched polymers in the raw materials, avoiding uneven raw materials or local defects. The barrel temperature of the extruder is controlled within the range of 190 - 240 °C. This temperature range helps the raw materials reach an appropriate fluidity while avoiding degradation caused by overheating. At this temperature, the base material, fillers, and other additives can be well dissolved and fused, ensuring the uniformity of the final product.

[0009] S3. Two - time injection molding: After arranging the inner sleeve ring in Mold 2, pour the molten raw materials into Mold 2 to form the outer sleeve ring, and the outer sleeve ring wraps the outer wall of the inner sleeve ring. Take it out after cooling to room temperature to obtain the electro - fusion sleeve.

[0010] During the two - time injection molding process, the inner sleeve ring has already wrapped the metal wire through the one - time injection molding process. The purpose of the two - time injection molding is to form the final electro - fusion sleeve shell. By injecting the molten raw materials into Mold 2 and making it wrap the inner sleeve ring, the finally formed electro - fusion sleeve has strength, sealing performance, and corrosion resistance. The purpose of the two - time injection molding is to protect the electro - fusion sleeve by forming a strong outer structure and also provide support for the inner sleeve ring.

[0011] Preferably, the base material includes one of high - density polyethylene, medium - density polyethylene, cross - linked polyethylene, or polypropylene.

[0012] Among them, high - density polyethylene (HDPE), medium - density polyethylene (MDPE), cross - linked polyethylene (PEX), or polypropylene (PP) has good mechanical properties, chemical stability, and weather resistance, and is the main component of the composite material. They provide strength, corrosion resistance, and long - term service life for the electro - fusion sleeve.

[0013] The filler includes graphene.

[0014] As a filler, graphene can not only enhance the mechanical properties of the composite material but also has good electrical conductivity and thermal conductivity. In the application of composite pressure pipes, the addition of graphene can improve the electrical conductivity of the pipeline, ensure the effective conduction of heat during electro - fusion connection, and enhance the stability of the connection.

[0015] The hyper - branched polymer includes one of hyper - branched polyamide, hyper - branched polyolefin, or hyper - branched polyether.

[0016] Hyperbranched polymers have a high degree of molecular branching, which makes them have excellent effects in enhancing material properties. They improve the rigidity, strength, and wear resistance of composite materials, contributing to the long-term stability of the materials.

[0017] The antioxidant includes one of phosphite antioxidants or thioester antioxidants.

[0018] Antioxidants are used to prevent the substrate from undergoing oxidation reactions during processing or long-term use. Phosphite antioxidants or thioester antioxidants can effectively prevent the degradation of polymers under high-temperature conditions and extend the service life of products.

[0019] Preferably, the lubricant includes one of ethylene bisstearamide, polytetrafluoroethylene micropowder, calcium stearate, or zinc stearate;

[0020] Lubricants reduce the friction of raw materials during injection molding, improve the fluidity of raw materials, prevent mold damage, and improve production efficiency.

[0021] The light stabilizer includes one of hindered amine light stabilizers or ultraviolet absorbers;

[0022] Light stabilizers are used to prevent material aging caused by ultraviolet rays. In the application of composite materials, especially in pipes exposed to the external environment, light stabilizers can ensure the durability of the materials.

[0023] The crosslinking agent includes one of vinyl silane crosslinking agents or aziridine crosslinking agents.

[0024] Crosslinking agents promote the crosslinking reaction of materials, enhance the thermal stability, mechanical properties, and chemical resistance of plastics. Especially in the application of electrofusion sleeves, crosslinking agents can enhance the rigidity and high-temperature resistance of the overall structure.

[0025] Preferably, the metal wire includes one of tungsten wire, nickel-chromium alloy wire, or copper-nickel alloy wire.

[0026] Preferably, the ratio of nickel to chromium in the nickel-chromium alloy wire is 7.5 - 8.5:1.3 - 2.3, and the ratio of copper to nickel in the copper-nickel alloy wire is 8.6 - 9.3:0.7 - 1.2.

[0027] The selection of metal wires plays a crucial role in the performance of electrofusion sleeves. Tungsten wire, nickel-chromium alloy wire, or copper-nickel alloy wire have excellent high-temperature resistance and electrical conductivity. Nickel-chromium alloy wire and copper-nickel alloy wire are particularly suitable for applications in high-temperature environments because they can withstand the high temperatures during the electrofusion process and achieve effective heat conduction during the electrofusion process. The ratio of the metal wire is set within a certain range to ensure good electrofusion conductivity and thermal stability, while avoiding unnecessary material waste or production instability due to too high a ratio of the metal wire.

[0028] Preferably, in the first injection molding, a mixing blender is used to mix the raw materials, with a stirring speed of 800 - 1500 rpm and a time of 5 - 15 min. An extruder is used to melt the raw materials, and the barrel temperature is 190 - 240 °C, with a heating time of 8 - 14 min.

[0029] Preferably, in S2, after preheating the first mold, the molten raw materials are poured in. The preheating temperature is 100 - 130 °C, and the cooling rate after the first injection molding is 10 - 30 °C / min.

[0030] Preferably, in S3, after preheating the second mold, the inner ring of the sleeve is placed in it. The preheating temperature is 190 - 240 °C.

[0031] Preferably, the ratio of the wall thickness of the inner ring of the sleeve to the wall thickness of the electrofusion sleeve is 0.4 - 0.7:1, and the ratio of the wall thickness of the outer ring of the sleeve to the wall thickness of the electrofusion sleeve is 0.3 - 0.6:1.

[0032] Preferably, the cooling rate in the second injection molding is as follows:

[0033] First stage: Cool at 3 - 5 °C / min for 20 - 30 min, and then proceed to the second stage of cooling;

[0034] Second stage: Cool at 10 - 30 °C / min to room temperature.

[0035] The control of the cooling rate is crucial for plastic molding. An excessively fast cooling rate will cause internal stress concentration in the material, possibly resulting in cracks or deformations; while an excessively slow cooling rate may lead to a reduction in production efficiency. By controlling the cooling rate, the best physical properties of the material can be ensured during the molding process. Especially in the second injection molding, the staged control of the cooling rate can better avoid stress concentration and ensure the uniformity and stability of the product. The slow cooling in the first stage (3 - 5 °C / min) helps the initial solidification of the material, while the faster cooling in the second stage (10 - 30 °C / min) can quickly reduce the temperature and stabilize the product structure.

[0036] The present invention provides a production process for an electrofusion sleeve part of a composite pressure pipe. It has the following beneficial effects:

[0037] 1. By using hyperbranched polymers with a highly branched molecular structure in the present invention, they can be evenly distributed in the matrix in the molten state, and at the same time, a dense cross-linked network is formed after cooling. Moreover, they have the characteristics of low viscosity and intermolecular interaction of high molecular chains, which can effectively improve the elongation at break of the material, enabling it to have excellent energy absorption capacity under external force, thereby enhancing the impact resistance.

[0038] 2. By using graphene as a filler, the present invention takes advantage of its ultra-high thermal conductivity and excellent mechanical properties. During the electrofusion connection process, graphene can rapidly transfer heat, reducing uneven fusion caused by local overheating or excessive temperature difference. Meanwhile, due to its ultra-high specific surface area and excellent interfacial bonding ability, it can form a high-strength support network within the polymer matrix, enhancing the tensile strength and wear resistance of the material.

[0039] 3. Through the synergistic effect of hyperbranched polymers and graphene fillers, the present invention utilizes the highly branched structure of hyperbranched polymers to provide a large number of crosslinkable sites, which physically entangle or chemically crosslink with the functional groups on the surface of graphene, forming a stable interfacial bonding layer. This enables graphene to be uniformly dispersed within the polymer matrix, while enhancing the network structure stability of hyperbranched polymers, further improving the fracture toughness and wear resistance of the material. At the same time, the high thermal conductivity of graphene makes the crosslinking process of hyperbranched polymers more uniform, avoiding the brittleness problem caused by local over-crosslinking.

[0040] 4. By adopting a staged cooling strategy, first slowly cooling down and then accelerating the cooling, the present invention precisely regulates the crystallization process of the material. The initial low-speed cooling at 3 - 5 °C / min helps the polymer chain segments to gradually rearrange, reducing the accumulation of internal stress during the cooling process, minimizing the generation of microcracks, and enabling the material to maintain high toughness and dimensional stability. Subsequently, the second-stage accelerated cooling at 10 - 30 °C / min can rapidly solidify the material, shorten the production cycle, and prevent excessive grain growth caused by long-term cooling, improving the uniformity of the final product. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 is a schematic flow chart of the method of the present invention;

[0042] Figure 2 is a schematic diagram of the sleeve structure after the first injection molding and the second injection molding of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0043] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the specification of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0044] For a better understanding of the present invention, the above content will be described in detail below in conjunction with specific embodiments.

[0045] Please refer to the attached Figure 1 and Figure 2 , the embodiments of the present invention provide a production process for composite pressure pipe electrofusion sleeve fittings;

[0046] Example 1:

[0047] S1. Prepare raw materials: 55 parts of base material (high-density polyethylene), 7 parts of filler (graphene), 3 parts of hyperbranched polymer (hyperbranched polyamide), 0.7 part of antioxidant (phosphite antioxidant), 0.4 part of lubricant (polytetrafluoroethylene micropowder), 1.5 parts of light stabilizer (hindered amine light stabilizer), 1 part of crosslinking agent (vinylsilane crosslinking agent), and 2 parts of metal wire 2 (tungsten wire);

[0048] Mixing of raw materials: Load the raw materials into a mixing blender and mix for 11 min at a rotation speed of 1000 rpm;

[0049] Heating of raw materials: Load the mixed raw materials into an extruder and heat for 12 min at a barrel temperature of 225 °C;

[0050] S2. First injection molding: Preheat mold 1 to 120 °C, and after the injection molding is completed, cool to room temperature at a cooling rate of 25 °C / min and take out to obtain the inner ring of the casing. Subsequently, sleeved the metal wire (tungsten wire) on the inner ring of the casing, and the ratio of the wall thickness of the inner ring of the casing to the wall thickness of the electrofusion casing is 0.5:1;

[0051] S3. Second injection molding: Preheat mold 2 to 200 °C, pour the molten raw materials after arranging the inner ring of the casing, and then cool to room temperature in stages and take out:

[0052] First stage: Cool at 4 °C / min for 25 min;

[0053] Second stage: Cool to room temperature at 15 °C / min;

[0054] And the ratio of the outer ring of the casing to the wall thickness of the electrofusion casing is 0.5:1.

[0055] Example 2:

[0056] S1. Prepare raw materials: 55 parts of base material (high-density polyethylene), 10 parts of filler (graphene), 4 parts of hyperbranched polymer (hyperbranched polyamide), 0.7 part of antioxidant (phosphite antioxidant), 0.4 part of lubricant (polytetrafluoroethylene micropowder), 1.5 parts of light stabilizer (hindered amine light stabilizer), 1 part of crosslinking agent (vinylsilane crosslinking agent), and 2 parts of metal wire (tungsten wire);

[0057] Mixing of raw materials: Load the raw materials into a mixing blender and mix for 11 min at a rotation speed of 1000 rpm;

[0058] Heating of raw materials: Load the mixed raw materials into an extruder and heat for 12 min at a barrel temperature of 225 °C;

[0059] S2. First injection molding: Preheat the first mold to 120 °C. After the injection molding is completed, cool it to room temperature at a cooling rate of 25 °C / min and take out to obtain the inner ring of the sleeve. Then, sleeved the metal wire (tungsten wire) inside the inner ring of the sleeve, and the ratio of the wall thickness of the inner ring of the sleeve to the wall thickness of the electrofusion sleeve is 0.5:1;

[0060] S3. Second injection molding: Preheat the second mold to 200 °C. After arranging the inner ring of the sleeve, pour in the molten raw material, and then cool it to room temperature in stages and take out:

[0061] First stage: Cool at 4 °C / min for 25 min;

[0062] Second stage: Cool to room temperature at 15 °C / min;

[0063] And the ratio of the wall thickness of the outer ring of the sleeve to the wall thickness of the electrofusion sleeve is 0.5:1.

[0064] Example 3:

[0065] S1. Prepare raw materials: Substrate (high-density polyethylene): 55 parts, filler (graphene): 5 parts, hyperbranched polymer (hyperbranched polyamide): 2 parts, antioxidant (phosphite antioxidant): 0.7 part, lubricant (polytetrafluoroethylene micropowder): 0.4 part, light stabilizer (hindered amine light stabilizer): 1.5 parts, crosslinking agent (vinyl silane crosslinking agent): 1 part, metal wire (tungsten wire) 2 parts;

[0066] Mix raw materials: Load the raw materials into a mixing blender and mix for 11 min at a rotation speed of 1000 rpm;

[0067] Heat raw materials: Load the mixed raw materials into an extruder and heat for 12 min at a barrel temperature of 225 °C;

[0068] S2. First injection molding: Preheat the first mold to 120 °C. After the injection molding is completed, cool it to room temperature at a cooling rate of 25 °C / min and take out to obtain the inner ring of the sleeve. Then, sleeved the metal wire (tungsten wire) inside the inner ring of the sleeve, and the ratio of the wall thickness of the inner ring of the sleeve to the wall thickness of the electrofusion sleeve is 0.5:1;

[0069] S3. Second injection molding: Preheat the second mold to 200 °C. After arranging the inner ring of the sleeve, pour in the molten raw material, and then cool it to room temperature in stages and take out:

[0070] First stage: Cool at 4 °C / min for 25 min;

[0071] Second stage: Cool to room temperature at 15 °C / min;

[0072] And the ratio of the wall thickness of the outer ring of the sleeve to the wall thickness of the electrofusion sleeve is 0.5:1.

[0073] Example 4:

[0074] S1. Prepare raw materials: 55 parts of base material (high-density polyethylene), 7 parts of filler (graphene), 3 parts of hyperbranched polymer (hyperbranched polyamide), 0.7 part of antioxidant (phosphite antioxidant), 0.4 part of lubricant (polytetrafluoroethylene micropowder), 1.5 parts of light stabilizer (hindered amine light stabilizer), 1 part of crosslinking agent (vinyl silane crosslinking agent), and 2 parts of metal wire (tungsten wire);

[0075] Mix raw materials: Load the raw materials into a mixing blender and mix for 11 min under the condition of a rotational speed of 1000 rpm;

[0076] Heat the raw materials: Load the mixed raw materials into an extruder and heat for 12 min under the condition of a barrel temperature of 225 °C;

[0077] S2. First injection molding: Preheat the mold one to 120 °C, and after the injection molding is completed, cool it to room temperature at a cooling rate of 25 °C / min and take out to obtain the inner ring of the casing. Subsequently, sleeve the metal wire (tungsten wire) on the inner ring of the casing, and the ratio of the wall thickness of the inner ring of the casing to that of the electrofusion casing is 0.4:1;

[0078] S3. Second injection molding: Preheat the mold two to 200 °C, pour the molten raw materials after arranging the inner ring of the casing, and then cool it to room temperature in stages and take out:

[0079] First stage: Cool at 5 °C / min for 20 min;

[0080] Second stage: Cool to room temperature at 30 °C / min;

[0081] And the ratio of the outer ring of the casing to the wall thickness of the electrofusion casing is 0.6:1.

[0082] Example 5:

[0083] S1. Prepare raw materials: 55 parts of base material (high-density polyethylene), 7 parts of filler (graphene), 3 parts of hyperbranched polymer (hyperbranched polyamide), 0.7 part of antioxidant (phosphite antioxidant), 0.4 part of lubricant (polytetrafluoroethylene micropowder), 1.5 parts of light stabilizer (hindered amine light stabilizer), 1 part of crosslinking agent (vinyl silane crosslinking agent), and 2 parts of metal wire (tungsten wire);

[0084] Mix raw materials: Load the raw materials into a mixing blender and mix for 11 min under the condition of a rotational speed of 1000 rpm;

[0085] Heat the raw materials: Load the mixed raw materials into an extruder and heat for 12 min under the condition of a barrel temperature of 225 °C;

[0086] S2. First injection molding: preheat the mold to 120 °C, and after the injection molding is completed, cool it to room temperature at a cooling rate of 25 °C / min and take out the inner ring of the sleeve. Then, sleeve the metal wire (tungsten wire) inside the inner ring of the sleeve, and the ratio of the wall thickness of the inner ring of the sleeve to the wall thickness of the electrofusion sleeve is 0.7:1;

[0087] S3. Second injection molding: preheat the second mold to 200 °C, pour the molten raw material after arranging the inner ring of the sleeve, and then cool it in stages to room temperature and take it out:

[0088] First stage: cool at 3 °C / min for 30 min;

[0089] Second stage: cool to room temperature at 10 °C / min;

[0090] And the ratio of the outer ring of the sleeve to the wall thickness of the electrofusion sleeve is 0.3:1.

[0091] Comparative example 1:

[0092] Based on Example 1, without filler (graphene), and the rest are the same.

[0093] Comparative example 2

[0094] Based on Example 2, where the filler (graphene) is 11 parts, and the rest are the same.

[0095] Comparative example 3

[0096] Based on Example 3, where the filler (graphene) is 4 parts, and the rest are the same.

[0097] Comparative example 4:

[0098] Based on Example 1, without hyperbranched polymer (hyperbranched polyamide), and the rest are the same.

[0099] Comparative example 5:

[0100] Based on Example 2, where the hyperbranched polymer (hyperbranched polyamide) is 5 parts, and the rest are the same.

[0101] Comparative example 6:

[0102] Based on Example 3, where the hyperbranched polymer (hyperbranched polyamide) is 1 part, and the rest are the same.

[0103] Comparative example 7:

[0104] Based on Example 1, without setting the first injection molding and the second injection molding, directly complete the injection molding at one time. Among them, preheat the second mold to 200 °C, pour the molten raw material after arranging the metal wire (tungsten wire), and then cool it in stages to room temperature and take it out: First stage: cool at 4 °C / min for 25 min; Second stage: cool to room temperature at 15 °C / min, and the rest are the same.

[0105] Comparative Example 8:

[0106] Based on Example 4, staged cooling: First stage: cool at 6 °C / min for 32 min; Second stage: cool to room temperature at 33 °C / min, and the rest are the same.

[0107] Comparative Example 9:

[0108] Based on Example 5, staged cooling: First stage: cool at 2 °C / min for 25 min; Second stage: cool to room temperature at 9 °C / min, and the rest are the same.

[0109] Experiment 1:

[0110] Experiment purpose:

[0111] This experiment aims to evaluate the roles of fillers (graphene) and hyperbranched polymers (hyperbranched polyamides) in electrofusion sleeve fittings of composite pressure pipes, and analyze their effects on the mechanical properties, thermal conductivity, impact resistance, and electrofusion connection stability of the materials.

[0112] Experimental sample setup: Use Examples 1, 2, and 3 as the main experimental groups for comparison, and use Comparative Examples 1, 2, 3, 4, 5, and 6 as the control groups.

[0113] Performance test:

[0114] 1. Tensile test:

[0115] Purpose: To determine the mechanical properties such as the tensile strength, yield strength, and elongation at break of the material.

[0116] Equipment: Use a universal material testing machine for testing.

[0117] Testing method:

[0118] Place the sample (with dimensions of 100 mm × 10 mm × 5 mm) in the fixture of the testing machine.

[0119] Set the test speed to 5 mm / min and start the test equipment.

[0120] Record the force value and deformation data of the sample during the tensile process until the sample breaks.

[0121] Calculate the tensile strength, yield strength, and elongation at break indexes according to the stress-strain curve.

[0122] Result analysis: Analyze the strengthening effect of graphene and hyperbranched polymers in the composite material, and focus on observing the tensile strength and elongation at break.

[0123] 2. Impact test:

[0124] Purpose: To evaluate the impact toughness of the material and determine its fracture resistance under external impact loads.

[0125] Equipment: Use an impact testing machine for testing.

[0126] Testing method:

[0127] Make the sample into a standard V-notch (size: 55mm×10mm×5mm).

[0128] Fix the sample on the bracket of the impact machine, ensuring that the notch surface faces the impact direction.

[0129] Start the impact testing machine, allow the standard impact hammer to hit the sample, and record the energy absorption value after damage.

[0130] Repeat the test three times and take the average value.

[0131] Result analysis: By analyzing the impact strength, evaluate the improvement effect of graphene and hyperbranched polymers on the impact toughness of the material, and observe their influence on material fracture.

[0132] 3. Thermal conductivity test:

[0133] Purpose: To measure the thermal conductivity of the material and evaluate the heat transfer efficiency of the material in a high-temperature environment.

[0134] Equipment: Use the laser flash method or the heat flow meter method for thermal conductivity testing.

[0135] Testing method:

[0136] Cut the sample into standard dimensions (usually 10mm×10mm×5mm).

[0137] Place the sample in the test area of the thermal conductivity testing instrument.

[0138] Start the equipment, irradiate the sample with a laser and measure the temperature change of the sample.

[0139] Calculate the thermal conductivity value through the algorithm provided by the equipment.

[0140] Result analysis: By comparing the thermal conductivities of different samples, observe how graphene and hyperbranched polymer fillers improve the thermal conductivity of the material to ensure uniform heat conduction during electrofusion connection.

[0141] 4. Electrofusion connection test:

[0142] Purpose: To test the connection stability of the electrofusion sleeve and the heat conduction effect during electrofusion to ensure the quality of electrofusion connection.

[0143] Equipment: Use a special electrofusion connection test device, usually equipped with a temperature control device, a pressure sensor, and a current monitoring system.

[0144] Testing method:

[0145] Connect two electrofusion casing samples according to the standard requirements to ensure complete contact in the joint area.

[0146] Apply the specified current and voltage to the sample to simulate the temperature rise and heat conduction during the electrofusion process.

[0147] Through temperature sensors and current monitoring devices, record the thermal changes during the electrofusion process in real time.

[0148] Evaluate the stability of the joint area and check for cracks, uneven fusion, or uneven heat.

[0149] After the test, confirm the stability of the electrofusion connection through visual inspection or disconnection test.

[0150] Result analysis: By comparing samples with different formulations, analyze how the filler graphene and hyperbranched polymer improve the thermal uniformity during the electrofusion process to ensure that there are no defects caused by excessive temperature difference or heat stress concentration at the connection site.

[0151] Table 1: Comparison table of performance test data of electrofusion casing parts of composite pressure pipes in Experiment 1

[0152]

[0153]

[0154] Experimental summary

[0155] 1. Tensile strength and elongation at break:

[0156] Example 1 (7 parts of graphene, 3 parts of hyperbranched polymer) and Example 2 (10 parts of graphene, 4 parts of hyperbranched polymer) have obvious advantages in tensile strength and elongation at break. The tensile strength of Example 1 is 35.0 MPa, and that of Example 2 is 38.2 MPa, while the tensile strength of Comparative Example 1 (no filler, 3 parts of hyperbranched polymer) is only 25.5 MPa, showing the significant role of the filler graphene and hyperbranched polyamide in improving the tensile strength and ductility of the material.

[0157] Example 3 (5 parts of graphene, 2 parts of hyperbranched polymer) also shows excellent performance, with a tensile strength of 33.0 MPa, which is significantly improved compared to the comparative example group, and the elongation at break also reaches 17%. This indicates that even low-content graphene and hyperbranched polymer formulations can significantly improve the tensile strength and ductility of the composite material.

[0158] Advantage analysis: The introduction of graphene improves the tensile strength and toughness of the composite material. Its excellent mechanical properties effectively disperse stress and enhance the structural stability of the material. The highly branched structure of the hyperbranched polymer further enhances the elongation at break and impact resistance of the material by forming a stable molecular network. The combination of the two greatly improves the tensile strength and ductility of the composite material.

[0159] 2. Impact strength:

[0160] The impact strength of Example 1 is 14.5 J, that of Example 2 is 15.2 J, and that of Example 3 is 13.8 J, all of which are much better than those of Comparative Example 1 (9.0 J) and Comparative Example 4 (6.5 J), and far exceed the performance of other comparative example groups. This indicates that the addition of the filler graphene and the hyperbranched polymer plays a crucial role in improving the impact resistance of the material.

[0161] The high strength and rigidity of graphene enable the composite material to better withstand impact loads, while the toughness and flexibility of the hyperbranched polymer help the material have better energy absorption capacity under impact, thus reducing the generation of fractures and cracks.

[0162] Advantage analysis: The high strength of graphene and the flexibility of the hyperbranched polymer jointly improve the impact resistance of the composite material. Under high impact loads, the material exhibits higher impact strength, reducing the risk of cracks or fractures.

[0163] 3. Thermal conductivity:

[0164] The thermal conductivity of Example 2 is 4.5 W / m·K, which is the best among all samples. In contrast, the thermal conductivity of Comparative Example 1 is 3.0 W / m·K, and that of Comparative Example 4 is 2.5 W / m·K. This indicates that graphene, as a filler in the composite material, significantly improves the thermal conductivity of the material, contributing to more uniform heat conduction during the electrofusion process.

[0165] The thermal conductivities of Example 1 (4.0 W / m·K) and Example 3 (4.2 W / m·K) are also much higher than those of the comparative example groups, showing that the addition of graphene improves the thermal conductivity of the material, ensuring uniform heat distribution during the electrofusion process and avoiding local overheating and thermal stress concentration.

[0166] Advantage analysis: The high thermal conductivity of graphene enables the composite material to conduct heat quickly and uniformly during the electrofusion process, ensuring the stability and uniformity of the electrofusion connection, thereby improving the overall performance of the electrofusion casing. The two-dimensional structure and high specific surface area of graphene enable it to conduct heat efficiently, enhancing the thermal stability of the material.

[0167] 4. Electrofusion stability:

[0168] The electrofusion stability of Example 2 is the highest, reaching 99.8%. In contrast, the electrofusion stabilities of Comparative Example 1 (91.5%) and Comparative Example 4 (85.0%) are significantly poorer. This indicates that the introduction of graphene and hyperbranched polymers significantly improves the stability of electrofusion connection, ensuring heat conduction and connection quality during the electrofusion process.

[0169] The electrofusion stabilities of Example 1 and Example 3 are 99.5% and 99.2% respectively, also showing very high stability, proving that this composite material can withstand higher temperature changes and current fluctuations in practical applications.

[0170] Advantage analysis: The excellent thermal conductivity of graphene and the toughness of hyperbranched polymers work together to ensure that during the electrofusion process, the material can evenly transfer heat, avoiding local overheating and stress concentration, thereby enhancing the stability of electrofusion connection. This is one of the key properties of electrofusion sleeves in practical use.

[0171] Through detailed analysis of the tabular data, it can be clearly seen that Example 1, Example 2, and Example 3 all show excellent performance in all test items, especially in terms of tensile strength, elongation at break, impact strength, thermal conductivity, and electrofusion stability. These advantages all stem from the synergistic effect of the filler graphene and the hyperbranched polymer hyperbranched polyamide:

[0172] Graphene improves the tensile strength, thermal conductivity, and impact strength of the composite material, ensuring uniform heat conduction during the electrofusion process and enhancing the overall strength and durability of the material.

[0173] The hyperbranched polymer, through its unique molecular structure, provides better toughness, ductility, and impact resistance, thus improving the elongation at break and impact strength of the material.

[0174] In contrast, the comparative example group failed to make full use of these excellent material properties, resulting in poorer performance in terms of mechanical properties, thermal conductivity, and electrofusion stability. Therefore, the production process of the composite pressure pipe electrofusion sleeve of the present invention has significant advantages in improving material properties and is particularly suitable for electrofusion sleeve applications that require high strength and high stability.

[0175] Experiment 2:

[0176] Experimental purpose: This experiment aims to compare the performance differences between Example 1 (using staged injection molding) and Comparative Example 7 (using one-shot injection molding) in the composite pressure pipe electrofusion sleeve, and verify the advantages of staged injection molding in terms of material mechanical properties, thermal conductivity, electrofusion stability, etc.

[0177] Experimental sample setting: Use Example 1 and Comparative Example 7 for comparison.

[0178] Performance test:

[0179] 1. Tensile test:

[0180] Purpose: To measure the mechanical properties of materials such as tensile strength, yield strength, and elongation at break.

[0181] Equipment: Use a universal material testing machine for testing.

[0182] Testing method:

[0183] Place the sample (size: 100mm × 10mm × 5mm) in the fixture of the testing machine.

[0184] Set the test speed to 5mm / min and start the test equipment.

[0185] Record the force value and deformation data of the sample during the tensile process until the sample breaks.

[0186] Calculate the tensile strength, yield strength, and elongation at break indexes according to the stress-strain curve.

[0187] Result analysis: Analyze the strengthening effect of staged injection molding in the composite material, and focus on observing the tensile strength and elongation at break.

[0188] 2. Impact test:

[0189] Purpose: To evaluate the impact toughness of the material and determine its fracture resistance under external impact loads.

[0190] Equipment: Use an impact testing machine for testing.

[0191] Testing method:

[0192] Make the sample into a standard V-notch (size: 55mm × 10mm × 5mm).

[0193] Fix the sample on the bracket of the impact machine, ensuring that the notch surface faces the impact direction.

[0194] Start the impact testing machine, allow the standard impact hammer to hit the sample, and record the energy absorption value after damage.

[0195] Repeat the test three times and take the average value.

[0196] Result analysis: Evaluate the improvement effect of staged injection molding on the impact toughness of the material by analyzing the impact strength, and observe its influence on material fracture.

[0197] 3. Thermal conductivity test:

[0198] Purpose: To measure the thermal conductivity of the material and evaluate the heat transfer efficiency of the material in a high-temperature environment.

[0199] Equipment: The thermal conductivity is tested using the laser flash method or the heat flow meter method.

[0200] Test method:

[0201] Cut the sample into standard dimensions (usually 10mm×10mm×5mm).

[0202] Place the sample in the test area of the thermal conductivity testing instrument.

[0203] Start the equipment, irradiate the sample with a laser and measure the temperature change of the sample.

[0204] Calculate the thermal conductivity value through the algorithm provided by the equipment.

[0205] Result analysis: By comparing the thermal conductivities of different samples, observe how the staged injection molding improves the thermal conductivity of the material and ensure the uniform conduction of heat during the electrofusion connection.

[0206] 4. Electrofusion connection test:

[0207] Purpose: Test the connection stability of the electrofusion sleeve and the thermal conduction effect during the electrofusion process to ensure the quality of the electrofusion connection.

[0208] Equipment: Use a special electrofusion connection test device, usually equipped with a temperature control device, a pressure sensor and a current monitoring system.

[0209] Test method:

[0210] Connect two electrofusion sleeve samples according to the standard requirements to ensure complete contact in the joint area.

[0211] Apply the specified current and voltage to the sample to simulate the temperature rise and thermal conduction during the electrofusion process.

[0212] Through the temperature sensor and current monitoring equipment, record the thermal changes during the electrofusion process in real time.

[0213] Evaluate the stability of the joint area and check for cracks, uneven fusion or uneven heat.

[0214] After the test, confirm the stability of the electrofusion connection through visual inspection or disconnection test.

[0215] Result analysis: Analyze how the staged injection molding improves the thermal uniformity during the electrofusion connection process to ensure that there are no defects caused by excessive temperature difference or thermal stress concentration in the connection area.

[0216] Table 2: Data table of comparative experiments between staged injection molding and one-shot injection molding process

[0217]

[0218] Experiment summary

[0219] Advantages of staged injection molding: The staged injection molding process (primary injection and secondary injection) in Example 1 ensures that during the injection molding process, the material can flow more evenly and avoids uneven internal stress or uneven heat conduction that may occur during the cooling process. The staged cooling process further reduces the accumulation of internal stress in the material during the molding process, ensuring the stability and high performance of the material. In contrast, Comparative Example 7 only uses primary injection molding and does not perform the secondary injection molding step, resulting in uneven material flow and possible stress concentration during the cooling process, thereby affecting its performance.

[0220] Differences in mechanical properties and thermal conductivity: From the data in the table, it can be seen that the tensile strength (35.0 MPa), impact strength (14.5 J), and thermal conductivity (4.0 W / m·K) of Example 1 are all significantly higher than those of Comparative Example 7. Staged injection molding enables the material to fully wrap the wire and cool evenly during the injection molding process, thereby improving the mechanical properties and heat conduction efficiency of the material. The lower performance of Comparative Example 7 indicates that the primary injection molding process cannot effectively avoid the internal stress of the material, resulting in poor mechanical properties and thermal conductivity.

[0221] Electrofusion stability: Electrofusion stability is a key indicator to measure whether an electrofusion casing can work stably under high temperature and high pressure environments. From the experimental results, the electrofusion stability of Example 1 is 99.5%, while that of Comparative Example 7 is 92.5%. Staged injection molding ensures more uniform heat conduction of the material, thereby better transferring heat during the electrofusion connection process and maintaining the stability of the connection. The primary injection molding process may lead to excessive temperature difference or uneven heat conduction, affecting the quality of the electrofusion connection.

[0222] Through this experiment, the significant advantages of the staged injection molding process over the primary injection molding process were verified. Staged injection molding not only optimizes the fluidity and heat conductivity of the material but also effectively reduces the problem of uneven stress during the cooling process, thereby improving the mechanical properties, thermal conductivity, and electrofusion stability of the material. These advantages will greatly improve its reliability and durability in practical applications, especially in electrofusion casing parts of composite pressure pipes that require high thermal stability and high mechanical properties.

[0223] Experiment 3

[0224] Experimental purpose: This experiment aims to verify the advantages of staged cooling on material properties regarding the performance differences among different cooling rates.

[0225] Sample setting: Select Example 4, Example 5, Comparative Example 8, and Comparative Example 9.

[0226] Performance test:

[0227] Performance test:

[0228] 1. Tensile test:

[0229] Purpose: To measure mechanical properties such as the tensile strength, yield strength, and elongation at break of the material.

[0230] Equipment: Use a universal material testing machine for testing.

[0231] Testing method:

[0232] Place the sample (size: 100 mm × 10 mm × 5 mm) in the fixture of the testing machine.

[0233] Set the test speed to 5 mm / min and start the test equipment.

[0234] Record the force value and deformation data of the sample during the tensile process until the sample breaks.

[0235] Calculate the tensile strength, yield strength, and elongation at break indexes based on the stress-strain curve.

[0236] Result analysis: Analyze the strengthening effect of stepwise cooling in the composite material, with a focus on observing the tensile strength and elongation at break.

[0237] 2. Impact test:

[0238] Purpose: To evaluate the impact toughness of the material and determine its fracture resistance under external impact loads.

[0239] Equipment: Use an impact testing machine for testing.

[0240] Testing method:

[0241] Make the sample into a standard V-notch (size: 55 mm × 10 mm × 5 mm).

[0242] Fix the sample on the bracket of the impact machine, ensuring that the notch surface faces the impact direction.

[0243] Start the impact testing machine, allow the standard impact hammer to hit the sample, and record the energy absorption value after damage.

[0244] Repeat the test three times and take the average value.

[0245] Result analysis: Evaluate the improvement effect of stepwise cooling on the impact toughness of the material by analyzing the impact strength, and observe its influence on the fracture of the material.

[0246] 3. Thermal conductivity test:

[0247] Purpose: To measure the thermal conductivity of the material and evaluate the heat transfer efficiency of the material in a high-temperature environment.

[0248] Equipment: Use the laser flash method or the heat flow meter method to measure the thermal conductivity.

[0249] Test method:

[0250] Cut the sample into standard dimensions (usually 10mm×10mm×5mm).

[0251] Place the sample in the test area of the thermal conductivity testing instrument.

[0252] Start the equipment, irradiate the sample with a laser and measure the temperature change of the sample.

[0253] Calculate the thermal conductivity value through the algorithm provided by the equipment.

[0254] Result analysis: By comparing the thermal conductivities of different samples, observe how staged cooling improves the thermal conductivity of the material and ensure uniform heat conduction during electrofusion connection.

[0255] 4. Electrofusion connection test:

[0256] Purpose: Test the connection stability of the electrofusion sleeve and the thermal conduction effect during electrofusion to ensure the quality of the electrofusion connection.

[0257] Equipment: Use a special electrofusion connection test device, usually equipped with a temperature control device, a pressure sensor and a current monitoring system.

[0258] Test method:

[0259] Connect two electrofusion sleeve samples according to the standard requirements to ensure complete contact in the joint area.

[0260] Apply the specified current and voltage to the sample to simulate the temperature rise and heat conduction during electrofusion.

[0261] Through the temperature sensor and current monitoring equipment, record the thermal changes during electrofusion in real time.

[0262] Evaluate the stability of the joint area and check for cracks, uneven fusion or uneven heat.

[0263] After the test, confirm the stability of the electrofusion connection through visual inspection or disconnection test.

[0264] Result analysis: Analyze how staged cooling improves the thermal uniformity during electrofusion connection to ensure that there are no defects caused by excessive temperature difference or heat stress concentration in the connection area.

[0265] Table 3: Data table of comparative experiments on staged cooling and different cooling rates

[0266]

[0267]

[0268] Experimental Summary

[0269] Tensile Strength:

[0270] Example 4 (38.0 MPa) and Example 5 (36.5 MPa) are significantly higher in tensile strength than Comparative Example 8 (32.5 MPa) and Comparative Example 9 (30.0 MPa). This difference indicates that staged cooling can better reduce the accumulation of internal stress caused by temperature difference during the cooling process, thereby enhancing the tensile strength of the material.

[0271] In Example 4, the first stage with a lower cooling rate (5 °C / min) and the second stage with a higher cooling rate (30 °C / min) ensure that the material gradually adapts to temperature changes during the cooling process, thus effectively avoiding structural defects or cracks that may occur during cooling. Therefore, the material shows more stable performance and higher strength in the tensile test.

[0272] Elongation at Break:

[0273] The elongation at break of Example 4 and Example 5 are 20% and 18% respectively, which are significantly higher than that of Comparative Example 8 (14%) and Comparative Example 9 (12%). The lower cooling rate in staged cooling can effectively avoid excessive internal stress in the material, enabling the material to maintain better ductility during the tensile process, thereby increasing the elongation at break.

[0274] In Comparative Example 8 and Comparative Example 9, due to the too high or uneven cooling rate, a large temperature difference was generated during the cooling process, resulting in non-uniform distribution of internal stress in the material and affecting the elongation.

[0275] Impact Strength:

[0276] The impact strengths of Example 4 and Example 5 are 15.0 J and 14.0 J respectively, which are significantly higher than that of Comparative Example 8 (11.5 J) and Comparative Example 9 (9.0 J). This further proves the enhancing effect of staged cooling on the impact strength of the material. During the cooling process, the lower initial cooling rate and the higher later cooling rate help the material to form a more uniform distribution in the internal structure, thereby enhancing the impact resistance.

[0277] For the samples of Comparative Example 8 and Comparative Example 9 using rapid cooling, due to the non-uniform distribution of internal stress, the material is prone to fracture or crack under impact loading, resulting in a significant decrease in impact strength.

[0278] Thermal Conductivity:

[0279] The thermal conductivities of Example 4 and Example 5 are 4.2 W / m·K and 4.0 W / m·K respectively, which are much higher than those of Comparative Example 8 (3.8 W / m·K) and Comparative Example 9 (3.6 W / m·K). The lower cooling rate makes the crystal structure of the material more uniform, which helps to improve the thermal conductivity of the material. Through staged cooling, especially at a lower initial cooling rate, the material can better maintain the continuity of its molecular structure, thus enhancing the thermal conductivity.

[0280] On the contrary, in Comparative Example 8 and Comparative Example 9, due to the stress concentration in the material during the cooling process, local defects may occur in the lattice structure, reducing the thermal conductivity of the material.

[0281] Electrofusion stability:

[0282] The electrofusion stabilities of Example 4 and Example 5 are 99.8% and 99.5% respectively, which are significantly higher than those of Comparative Example 8 (95.0%) and Comparative Example 9 (92.0%). During the electrofusion process, the staged cooling process ensures the thermal uniformity and stability of the material during the cooling stage, thus improving the performance of the electrofusion casing. The uniformity and low internal stress of the material are crucial for the uniform distribution of heat during the electrofusion process.

[0283] The lower electrofusion stabilities of Comparative Example 8 and Comparative Example 9 indicate that due to the too high cooling rate, the heat distribution in the material during the electrofusion process is uneven, and local overheating or fracture may occur, thus affecting the stability of its electrofusion connection.

[0284] The optimization effect of staged cooling on material properties

[0285] Judging from the experimental data, the staged cooling process significantly improves multiple performance indexes of the material. The performance advantages of Example 4 and Example 5 show that staged cooling not only helps to improve the tensile strength, elongation at break and impact strength of the material, but also effectively improves the thermal conductivity and electrofusion stability of the material.

[0286] During the cooling process of Example 4 and Example 5, the temperature of the material is gradually reduced through different cooling rates, making the internal stress distribution of the material more uniform and avoiding stress concentration caused by too fast cooling. This cooling process effectively improves the mechanical properties of the material, especially significantly improves the tensile and impact properties. In addition, staged cooling makes the crystal structure of the material more stable, thus improving the thermal conductivity and electrofusion stability.

[0287] In contrast, the cooling rates adopted in Comparative Example 8 and Comparative Example 9 are relatively fast, resulting in uneven distribution of internal stress in the material, which in turn affects its mechanical properties and thermal conductivity. In addition, the higher cooling rate leads to the accumulation of thermal stress, reducing the stability of the material during the electrofusion process.

[0288] Experimental conclusion

[0289] The staged cooling process significantly improves the material properties: Experimental data show that Examples 4 and 5 with staged cooling exhibit excellent performance in terms of tensile strength, elongation at break, impact strength, thermal conductivity, and electrofusion stability, far exceeding those of Comparative Examples 8 and 9.

[0290] Cooling rate control is crucial: A lower cooling rate helps the material to have a uniform stress distribution during cooling, avoiding the problem of internal stress concentration, thereby improving the mechanical properties and thermal conductivity.

[0291] Electrofusion stability is a key advantage of staged cooling: By optimizing the cooling process, staged cooling ensures the uniform conduction of heat during the electrofusion process, significantly improving the electrofusion stability of the material and reducing local overheating and damage phenomena during electrofusion.

[0292] In summary, the staged cooling process has significant advantages in optimizing material properties, especially in terms of mechanical properties, thermal conductivity, and electrofusion stability, which are crucial for improving the reliability and durability of electrofusion sleeves.

[0293] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A production process of an electrofusion sleeve fitting for a composite pressure pipe, characterized in that, It includes the following steps: S1. Prepare raw materials, and the raw materials include the following components in parts by mass: substrate: 50 - 60 parts, filler: 5 - 10 parts, hyperbranched polymer: 2 - 4 parts, antioxidant: 0.5 - 1 part, lubricant: 0.2 - 0.5 part, light stabilizer: 1 - 2 parts, crosslinking agent: 0.5 - 2 parts, metal wire: 1 - 3 parts; S2. First injection molding, mix the raw materials and heat them to melt, then pour the molten raw materials into mold one, take them out after cooling to room temperature to obtain the inner ring of the sleeve. Then, sleevethe metal wire on the inner ring of the sleeve, and metal wires are arranged on both sides of the inner wall of the inner ring of the sleeve; S3. Second injection molding, after arranging the inner ring of the sleeve in mold two, pour the molten raw materials into mold two to form the outer ring of the sleeve, and the outer ring of the sleeve wraps the outer wall of the inner ring of the sleeve. Take them out after cooling to room temperature to obtain the electrofusion sleeve.

2. The production process of an electrofusion casing for a composite pressure pipe according to claim 1, characterized in that, The substrate includes one of high - density polyethylene, medium - density polyethylene, cross - linked polyethylene or polypropylene; The filler includes graphene; The hyperbranched polymer includes one of hyperbranched polyamide, hyperbranched polyolefin or hyperbranched polyether; The antioxidant includes one of phosphite antioxidants or thioester antioxidants; 3. The production process of an electrofusion casing for a composite pressure pipe according to claim 1, characterized in that, The lubricant includes one of ethylene bisstearamide, polytetrafluoroethylene micro - powder, calcium stearate or zinc stearate; The light stabilizer includes one of hindered amine light stabilizers or ultraviolet absorbers; The crosslinking agent includes one of vinyl silane crosslinking agents or aziridine crosslinking agents; 4. The production process of an electrofusion sleeve fitting for a composite pressure pipe according to claim 3, characterized in that, The metal wire includes one of tungsten wire, nickel - chromium alloy wire or copper - nickel alloy wire; 5. The production process of an electrofusion casing for a composite pressure pipe according to claim 4, characterized in that, In the nickel - chromium alloy wire, the ratio of nickel to chromium is 7.5 - 8.5:1.3 - 2.3, and in the copper - nickel alloy wire, the ratio of copper to nickel is 8.6 - 9.3:0.7 - 1.

2.

6. The production process of an electrofusion casing for a composite pressure pipe according to claim 1, characterized in that, In the first injection molding, a mixing blender is used to mix the raw materials, the stirring speed is 800 - 1500 rpm, and the time is 5 - 15 min. An extruder is used to melt the raw materials, the barrel temperature is 190 - 240 °C, and the heating time is 8 - 14 min.

7. The production process of an electrofusion sleeve for a composite pressure pipe according to claim 6, characterized in that, In S2, after preheating mold one, pour the molten raw materials. The preheating temperature is 100 - 130 °C, and the cooling rate after the first injection molding is 10 - 30 °C / min.

8. The production process of an electrofusion casing for a composite pressure pipe according to claim 1, characterized in that, In S3, after preheating mold two, put the inner ring of the sleeve into it. The preheating temperature is 190 - 240 °C.

9. The production process of an electrofusion casing for a composite pressure pipe according to claim 8, characterized in that, The ratio of the wall thickness of the inner ring of the sleeve to the wall thickness of the electrofusion sleeve is 0.4 - 0.7:1, and the ratio of the wall thickness of the outer ring of the sleeve to the wall thickness of the electrofusion sleeve is 0.3 - 0.6:

1.

10. The production process of an electrofusion casing for a composite pressure pipe according to claim 1, characterized in that, The cooling rate in the second injection molding is: First stage: Cool at 3 - 5 °C / min for 20 - 30 min, and then carry out the second - stage cooling; Second stage: Cool to room temperature at 10 - 30 °C / min.

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